Duplex facsimile



` Sept 2 1941- R. R. HAUGH 2,254,803

DUPLEX FACSIMILE Filed sept. 5, 1959 2 sheets-sheet 1 !F|c1unE"` Psmwavz SCANNER HMPWIIM:/hvnmmanl summe SYN. ELEMENT Mm'. MMT Comamen Plcrun'" Y PeAnWAvE SCANNER HnLrwAveAMPunen l Supmm Sept. 2, 1941.

' R. R. HAUGH DUPLEX FACSIMILE Filed Sept. 5, 1939 2 She REcTl FIER DIVIDER RADIoAMP.

Realmen- SuPPnesseR ets-Sheet 2 1 PLATE M.A.

5o |00 lso PLATE VQI-TS Fiel INVENTR Patented Sept. 2, 1941 STATES 4y Claims.

My invention pertains to the transmitting, receiving and recording of two shaded pictures simultaneously over a singlewire circuit or a radio carrier wave.

It has been known to the art to which this presen't invention relates, that a picture can be scanned by a beam of light and a phototube into areas and the light o each scanned area can be converted into electrical signals, or picture signals which are proportional to the intensity of the white and black picture elements and can be transmitted. At the receiving end the electrical impulses or picture signals are reconverted into picture elements, the value of which bears a direct relation to the signalling energy and are assembled in the same order as the original picture. By the term picture is included all printed matter, paintings, photographic negatives and the like.

In a facsimile transmitter, receiver and recorder, the long white or black picture areas are not sent as one continuous modulated signal but are converted by the use of a rotating scanning chopper disc, reed light valve, or multivibrator intodot keying. Thus, the scanned picture is resolved into dots or picture elements and each picture is sent as a separate picture, signals. The vhigher the keying frequency the smaller the picture area represented.

One of the new and novel features, of my invention, deals with the breaking up of two pictures into separate elements and to transmit a picture element from one picture and then from the other. In this system every other picture element of each picture is transmitted. Another novel feature of my invention deals with a new method for modulating a radio carrier wave, with two sets of `picture elements and a synchronizing signal. For example, Vthe alternations on one side of an alternating current are modulated by the light and dark areasY of one picture, the alternations on theV other side of the said alternating current are modulated by the light and dark areas of the other picture. The peaks of these modulated alternations are suppressed to the same level, leaving only the width of the alternations to represent the. light and dark areas of thepictures. These two sets of modulated rectangular waves are combined forming an alternating current with rectangular alternations with variable widths. In series with this alternating current is a D. C. voltage which shifts the axis of the alternating current soy that it isa pulsating D. C. voltage of theA same gensine wave of the samefrequency and in phase with the rectangular alternating current, thus, the rectangular waves are extended farther from their common axis due to this increase in voltage. As the envelope voltage of this combined wave does not reverse, it can be used for modulating a radio frequency carrier wave. In this radio carrier wave will be the modulated rectangular waves of each picturer and a synchronizing voltage. In this system the blacker the area scanned the greater the modulation. When two white areas are being scanned the alternations are not modulated, in this case the final wave is a pulsating sine wave.

Another new and novel feature of my invention resides in a receiver that will respond to the combined two sets of picture signals and acontinuous synchronizing signal and can divider out eachiset of'picture elements, for its own recorder and controls: the recording of the shading of each picture an'ddrives the recorder in synchronism with theltransmitted picture.

The object of this invention is to provide' a simple system for transmitting, receiving, cording and synchronizing two pictures at the same time. y

Another object of this invention resides in the constructionand the arrangement of the mechanical andelectrical parts as will be understoodrfrom the following specification, in connection with. the accompanying drawings which will illustrate one embodiment of my invention by way of example. In the accompanying drawings like reference numerals designate corresponding parts throughout.

Figure 1 is a schematic block diagram showing the general arrangement of the elements and amplifiers in this duplex facsimile system.

Figure 2 shows schematicjlayout of the circuit diagram ofthe duplex facsimile amplifiers.

Figure 3 showsthe efect that shading of the pictures has ondiferent'parts of the amplifier. Figure 4 shows the envelopes of the output of thev amplifier for various types of voltages.

Figure 5 is aschematic block. diagram showing the general arrangement of a duplex facsimile receiver. y

Figure 6 shows the schematic layout ofthe receiver circuit diagram. f y Figure 7 shows a modified form ofV a recorder for oneV picture-with two recording elements.

Figure -8 is an example of aA radiofca-rrier wave,

which contains the picture elements of lthe two eral form. In series with. this. combination is: a pictures anda synchronizing freqllelly..

Figure 9 is a rectified signal of radio carrier waves shown in Figure 8.

Figure shows the separate picture elements of both pictures.

Figure 11 shows the synchronizing voltage.

Figure 12 shows the plate current and plate voltage relationship of a pentode tube.

'Ihe general operating features of this duplex facsimile system are as follows:

The block diagram Figure 1 shows that synchronous motor drives two scanners and a high frequency generator. This generator supplies the high frequency keying voltage through two half wave rectiers, one for each amplier. One ampliler receives one alternation and the other amplifier receives the other alternation of the said keying voltage. The scanners pick up the light Variations due to the shading of the picture elements and modulate the rectified keying alternations. The peaks of these alternations are suppressed to a low and equal value. The two sets of suppressed peaks are combined forming an alternating current, which is combined with a high frequency current from the generator of the same frequency and in phase with each other. In Figure 2 the synchronous motor I drives the high frequency generator 2 and the two scanning drums 3 and 3. 'I'he light from lamp 4 is focused by lens 5 on the revolving scanning drum 3 on which is mounted picture .A. The light from picture A is reiiected into phototube 6 which is connected in series with the battery voltage 'I and the high resistance 8. The resistance 8 is connected between the grid 9 and the cathode Il] of the three element vacuum tube II. An increase in the amount of light due to a white area of picture A reflected into the phototube 6 will cause an increase in the current through the resistance 8, and an increase in the negative voltage on the grid 9 of tube I I and a decrease in the plate current I2. A black area on picture A will decrease the reflected light into phototube 6 and a decrease in the current through resistance 8 and a less negative voltage on the grid 8 of vacuum tube II which will increase conductivity of the plate circuit. In the plate circuit of tube I I is the secondary winding VI3 of transformer I4 which is connected to high frequency generator 2 and resistance I5 Vand battery voltage I6. The biasing voltage of tube II is so adjusted that when a white area of picture A" is being scanned the tube I I is biased to the cutol point so that no current from the secondary I3 of transformer I4 will flow through the plate circuit. As the reflected light is reduced due to the scanned portion becoming darker the bias is reduced and the peak currents from secondary I3 will iiow in the plate circuit. When the scanned portion is black the maximum peak current ofV one side of the high frequency wave is rectied. VThis modulated rectified half wave will flow through the resistance I5 and the voltage drop across resistance I5 will operate the amplifier tube I6. An increase in the plate current of tube I I due to a dark area of picture A will cause a positive voltageincrease on the grid I'I of tube I6. This will cause more current to ow in the plate circuit of tube I6 and a greater drop in voltage across the resistance I8. The pentode tube I9 is operated by the drop in voltage across resistance I8. The general operating characteristics of a pentode tube are shown in Figure 12, in this tube if the plate voltage is increased above a certain point the plate current does not increase to any extent. In series with the pentode tube I9 and the resistance I8 is resistance 20. When the peak voltage in resistance I8 increases beyond a certain value the plate current in tube I9 and through the resistance 20 will not increase any more, thus the voltage across resistance 20 will not increase for higher voltages across resistance I 8. The voltage across resistance 20 is at for these high values.

The lower amplifier in Figure 2 is constructed and operates the same as the upper amplifier that has just been described. Picture B is mounted on scanning drum 3. Battery 2| is in the plate circuits of both tubes I9 and I9 and is so adjusted that plate current in both these tubes are near the knee of the curve shown in Figure l2, as both tubes have the sarneoperating characteristics the voltage drop due to these continuous currents through resistances 20 and 2D' will balance each other. The increase in currents in each amplifier due to dark picture elements of equal value will not balance out because one ampliiier operates on one half of the waves and the other amplifier on the other half of the waves, from transformer I4. Resistance 20 which has the voltage variations across it that correspond to the picture elements of picture A and is connected in series with the resistance 20', which has the voltage variations across it that correspond to the picture elements of picture B but of opposite phase. These voltages across 20 and 20' combine and produce an alternating current 33 with varying alternation widths, and constant amplitude. This will be described later.

The transformer 22 which carries the synchronizing signal is connected to generator 2 and to the same frequency that operates transformer I4. The secondary 23 of transformer 22 is connected in series with resistances 29 and 20 so that the voltages across the resistance 20 are in phase with one half of the waves and the voltages across resistance 20 are in phase with the other half of the waves from secondary 23. The result is that the voltages of both alternating currents add together producing a very complicated wave form.

In series with resistances 20 and 28 and secondary 23 is a battery voltage 24 which is used to make a pulsating D. C. voltage out of the combined alternating currents from resistance 20 and 28 and the synchronizing Voltage of secondary 23. This pulsating D. C, voltage appears across the terminals A25 and 26 and can be used to modulate a carrier wave or be used to modulate the radio transmitter 21. l

In Figure 3 the area 28 represents a shaded section of picture A going from white to black. The triangle 29 represents the voltage variation across the resistance 8 due to reected light from the shadedsection 28 and this voltage is applied to the grid 9 of tube II. The A. C. wave 30 represents the keying voltage that is applied to the plate I2 of tube -II from the secondary I3 of the transformer I4 which is connected to generator 2. The plate current that ows through resistance I5, due tothe change in grid voltage and the A. C.,voltage in the plate circuit, produces the voltage variations as shown in 3I. For example thelwhite area in 28 produces no voltage on the grid Il of tube I6; the black area produces the maximum positive voltage While the shaded areas between integrate the voltages between zero' andV maximum.L The voltage shapes shown in 3| are amplified to proportionately high peak valu by the tube I6 with'corresponding large voltage variations across resistance I8. These voltages are applied to the plate of the pentode assises tube I9 which holds the plate current that flows through resistance 2U constant, when these voltages across resistance I8 reach a predetermined value. The result of this current control through resistance 25 is shown by the rectangular wave alternations shown in 32. In this case the peak voltages are constant and the width of the alter-A nations are the same as the widths shown in 3|. The light and dark areas of 23 are represented by the width of the rectangles shown in 32. The shaded area 28 produces the same general effect through the lower amplifier that the shaded area 28 did through the upper ampliiier but in this case the shaded area 28 is reversed, that is the black area is scanned rst and the white area last, so that the voltage in 29 decreases.- The combined rectangular alternate voltages across both resistances 20 and 29 are shown in 33, the rectangular voltages above the line represent picture A and the rectangular voltages below the line represents picture 13.

The result of placing only the battery voltage 24 across the terminals 25 and 25 for a period of time is shown by the rectangular envelope 34 in Figure 4. The results of placing the battery voltage 24 and the A. C. synchronizing voltage 3i) from secondary 23 across the terminals 25 and 26 are shown by envelope 35. The results of putting the voltage variations across the resistances 2-0 and 20 in series and in phase with the A. C.

synchronzing voltage 35 from secondary 23 and the battery voltage 24 are shown by envelope 35. The high rectangular peak areas 36' represent the shaded picture elements of picture A, the zero rectangular peak areas 35" represent the shaded picture elements of picture B, the curves in the center are part of the synchronizing voltage 30. If both the pictures A and B were white the rectangular portions 3S and 35 of the envelope 36 would disappear and only the synchronizing wave 35 plus the battery voltage 24 would be left as illustrated in envelope 35.

The block diagram in Figure shows the general arrangement of the duplex facsimile' receiver and recorder. The incoming radio carrier Wave is amplified and a part of this amplied signal is rectied and the different picture signals separated and amplified and recorded, respectively. Part of said amplified signal is rectified and the picture envelopes suppressed leaving only the synchronizing frequency which is amplified and operates a synchronous motor that drives the two recording drums.

A schematic circuit diagram of the receiver is shown in Figure 6 in which 49 represents the radio amplier which is inductively coupled by transformer 4i to the full wave rectifier 42. The output of this rectifier tube 42 is connected across the fixed terminals of resistance 42a. For the sake of simplicity no nlter circuit is shown in the output of the rectifier tube 42. The sliding contact 43 on resistance 42a is connected in series with the potentiometers 44 and 45, which is connected back to resistance 42a at point 45. The upper point of potentiometer 44 is connected to the positive terminal of battery 41, the negative terminal is connected to the grid 43 of tube 59, the lower point of potentiometer 45 is connected tothe negative terminal of battery 5I and the positive terminal is connected to the grid 52 of tube 53. The cathode 54 of tube 50 is connected to the sliding contact 55 of potentiometer 44. The cathode 55 of tube 53 is connected to the sliding contact 51 of potentiometer 45. The plate 58 of tube 50 is connected to recorder 59 which reproduces pictureV A on drum 13. The plate 69' of tube 53 is connected to the recorder 6I which reproduces picturer B on drum 12. The connecting point between the two potentiometers 44 vand 45 is connected to plate battery 62,*the other side of this battery is connected to both picture recorders 59 and 6|.

The rectifier tube 63 is inductively coupled to transformer 4| by winding 64. The output of tube'63 is connected by pushpull transformer 65 to the plates ofthe pentode tubes 66 and 61. The output ofthese tubes is connected by the pushpull transformer 68 to the two power tubes 69 and 10 which operate the synchronous motor 'H which drives the two scanning drums 12 and 13 in synchronism with scanning drums 3 and 3 as shown in Figure 2. Scanning drum 12 carries the reproduced picture B and scanning drum 13 carries the reproduced picture A.

If the two phototubes 6 and 6' shown in Figure 2 were scanning the same picture, one scanning point being ahead of the other, the same transmitting and receiving equipment could be used for transmitting and receiving one picture. The

, recording equipment would have to be changed,

that is the two recording drums 12 and 13 would have to be replaced by a single drum 14 as shown in Figure '1, and the two recorders 59 and 6l would have to be spaced the same distance apart as the two scanning points.

The advantage oi this system is that fading due to long distance transmission of the carrier waves would not affect the recording of the picture as much as in a single recording system because the chances of two fadings occurring at a definite time apart are small. If one phototube is sensitive to one color and the other phototube is sensitive to another color and the corresponding recorder reproducing these colors, it is possible to transmit a colored picture with this system. This system of transmission would be advantageous during war inasmuchV as that planes could transmit a picture or information at twice the speedl and if transmitted on two diierent radio wave lengths the chances of getting through would be many times greater because of the difflculty of interfering with both radio waves at the same time.

The envelope 56 shown in Figure 4 is used to modulate a radio carrier wave and will reproduce a radio frequency carrier wave envelope as shown in Figure 8. This radio wave is ampliiied by radio amplier 49 shown in Figure 6 then it is rectified by rectifier tube 42. This rectied voltage is applied across the resistance 42a and has an envelope form as shown in Figure 9. The general voltage amplitude of this envelope is regulated by sliding contact 43 and is applied acrossl the potentiometers 44 and 45. The positive voltage due to the drop in potential caused by the venvelope voltageV across the potentiometer 44 is regulated by the sliding contact 55 and is applied tothe grid of tube 553. The envelope voltage inFigure 9 would be reproduced again except for the battery vvoltage 41 biasing the grid 49 of tube 55 for values under the line 15 below the cutoi value of the tube. Thus, the rectangular value above the line 15 representing the dark areas in picture A is reproduced in the plate circuit of tube 5) which operates the recorder 59 which records the picture A on the synchronized drum 13.Y These picture elements represented by the variations in the plate current are shown by envelope 19 in Figure 10. The negative voltage due to the drop in potential caused by the envelope voltage shown in Figure 9 across the potentiometer 45 is regulated by contact 51 is applied to the grid 52 of tube 53. The envelope voltage shown in Figure 9 applied across the potentiometer 45 would be bias tube 56 beyond the cutoif point, for all values except for the positive bias of battery 5| which is so adjusted for all values under the line 16 representing dark areas in picture B are reproduced in the plate of tube 53. Thus, the rectangular values under the line 16 are reproduced in the plate circuit of the tube 53 which operates recorder 6| which records the picture B on the synchronized drum 72. These picture elements represented by the variations of plate currents are shown in envelope 80, Figure 10.

In this system of transmitting two pictures simultaneously, by the breaking up Aof each picture into picture elements, by means of the alternations of a keying frequency, it is obvious when one picture element is being transmitted from one picture the corresponding picture element of the other picture is suppressed, thus, every other picture element of each picture is transmitted. The size of the picture element is determined by the frequency of the keying voltage.

The tube 50 operates on the Value of the positive voltage above the line 75 and tube 53 operates on negative voltage below the line '16. In other words tubes 50 and 53 operate on the dark or shaded elements, the amount of shading depends upon the width of the rectangular waves, shown in picture ID. When a white area is being scanned in picture A, as shown in Figure 2, no signal will appear above the line l5, and when a white area is being scanned in picture B no signal will appear below the line 16. The only signal that will come through under the above conditions will be the synchronizing voltage that operates within the lines 'i5 and 'i6 which will not operate either of the tubes 50 or 53.

The synchronizing voltage is picked up by coil 64 and operates the rectifier tube 63. The result of this rectification is shown by envelope in Figure 9. This rectified voltage is applied to the plates of the two pentodes 66 and 6l by the transformer 65. After going through the transformer 65 the axis of the envelope is shifted from line 'l1 to line 18. This modulated A. C. wave is applied to the plates of tubes 65 and 61 which are adjusted so that values above l5 will not go through the tube 66 and values below 16 will not go through tube 6l. The wave in the primary winding of transformer 68 will look like Figure 11 which corresponds to Figure 9 with the rectangular voltage extensions removed. Figure 12 gives the plate voltage and plate current curve for pentodes tubes. The tubes 66 and 61 are so adjusted that when the plate voltages have reached values corresponding to the line 'l5 and 76, the tubes have reached the knee of the curve as shown in Figure 12 and for voltagesV above this point there is little if any increase in the plate current. The resulting wave is not a sine wave but it can be improved by transformer 68 or by using a lter before applying the voltages to the power tubes 63 and l0 which operates and keeps the synchronous motor 1| in step with the frequency from generator 2 as shown in Figure 2 so that the drums l2 and 'I3 operate in synchronism with the scanners 3 and 3.

I have chosen the particular embodiments described above as illustrative of my invention, and it will be apparent that various other modications may be made without departing from the spirit and scope of my invention, which modifications I aim to cover by the appended claims.

I claim as my invention:

1. A method of transmitting two shaded pictures simultaneously adding a constant amplitude variable time duration keying impulse corresponding to the shading intensity of one picture to one half of the alternations of a synchronizing signal, adding a constant amplitude Variable time duration keyingimpulse corresponding to the shading intensity of the other picture to the other half of the alternations of the said synchronizing signal, combining all said signals and impulses, and modulating a carrier.

2. A two picture radio carrier wave synchronizing transmitting system, comprising means for generating a synchronizing signal, means for adding to one half of the peaks of the said synchronizing signal a constant voltage keying signal whose width varies as the shading intensity of the scanned picture, a means for adding to the other half of the peaks of said synchronizing signal a constant voltage keying signal whose width varies as the shading intensity of a second scanned picture, means for modulating a radio carrier wave with the combined said synchronizing signal and the two said picture keying signals, and applying said signals for synchronizing and simultaneously recording said pictures.

3. A method of transmitting two independent and separate shaded pictures alternately, comprising generating a sustained synchronizing signal, separating the positive and negative alternations, keeping the amplitude constant and controlling the duration of the said positive and negative alternations with the shading of the said separate pictures, generating a radio carrier, applying controlled alternations so that the positive alternation eiects only an increase in the amplitude of the said radio carrier and the negative alternation effects only a decrease in the amplitude of the said radio carrier.

4. A method of transmitting two shaded pictures which comprises generating a synchronizing wave, modulating separately the positive and negative altern-ations of the said synchronizing wave in accordance with the variations of the light intensities from the said two shaded pictures, using the said modulated alternations t0 control the duration of picture signals, the amplitude of said picture signals remaining constant, adding the said picture signals to corresponding alternations of said generated sine wave, modulating a transmitter carrier with both the said synchronizing wave, and the said synchronizing wave plus the said picture signals.

RAYMOND R. HAUGH. 

